Filter Device, Particularly Reflux Vacuum Filter, and Filter Element For Such A Filter Device

ABSTRACT

The invention relates to a filter device, in particular a reflux vacuum filter, having at least one filter housing ( 7 ) in which at least one filter element ( 3 ) can be accommodated, the filter element defining a longitudinal axis ( 25 ), and having at least two valve units, particularly in the form of a bypass valve (V 2 ) and of a pre-pressurizing valve (V 1 ). The invention is characterized in that the valve units are arranged concentric to the longitudinal axis ( 25 ) of each filter element ( 3 ) along said longitudinal axis ( 25 ).

The invention relates to a filter device, particularly a reflux vacuum filter, with at least one filter housing in which at least one filter element which defines a longitudinal axis can be accommodated, and with at least two valve units, particularly in the form of a bypass valve and a back pressure valve. Moreover, the invention relates to a filter element for such a filter device.

Reflux vacuum filters of the aforementioned type are known. One device of this type which is marketed by the company ARGO-HYTOS GmbH is commercially available under the type designation E084. Reflux vacuum filters are used in hydraulic systems in those cases in which in the system there are both an open hydraulic circuit (such as working hydraulics) and also a closed hydrostatic system (for example, a traveling mechanism). Reflux vacuum filters here can assume both the function of the reflux filter of the open circuit and also the function of the vacuum filter of the closed circuit (mechanism), assuming that the reflux flow of the open hydraulic system is not smaller than the volumetric flow of the feed pump for the hydrostatic system.

In the operation of these devices the reflux amount, for example, of the working hydraulics, is supplied to the filter and is purified by the filter medium of the filter element, and full-flow extremely fine filtration can take place. In the filtered fluid which is available to the feed pump of the hydrostatic system, a preload pressure is maintained by the back pressure valve and ensures that the amount of filtered reflux required by the feed pump of the compensator can be removed. Excess amounts travel via the back pressure valve to the tank connection and are drained towards the tank. At high dynamic pressures which are caused, for example, by fouling at the filter element, a pressure decrease takes place by triggering of the bypass valve.

The object of this invention is to make available a filter device of the type under consideration, whose construction enables easy installation in the pertinent hydraulic systems, especially also with restricted space conditions under which only limited installation space is available.

According to the invention, this object is achieved by a filter device having the features of claim 1 in its entirety.

Accordingly, an important particularity of the invention consists in that all the main components are arranged concentrically to the longitudinal axis of the filter element. The overall device can form a slender, uniform body, for example, in an extended cylindrical shape without there being assemblies that protrude laterally on the body or which are offset to the longitudinal axis, for example, in the form of a bypass valve located laterally to the cylindrical body.

In advantageous exemplary embodiments there is also a third valve unit, specifically in the form of a replenishing valve, in an arrangement which is concentric to the longitudinal axis of the filter element. Without departing from the in-line construction, this ensures that when the reflux pressure fails, an amount of fluid can travel by way of the replenishing valve from the tank to the intake side of the feed pump of the hydrostatic circuit in the manner of an emergency function, so that, for example, the connected traveling mechanism does not fail.

In especially advantageous exemplary embodiments in which the filter housing has a head-side cover part with fluid guides which border the upper end region of the inserted filter element as well as at least one filter input for reflux fluid and at least one filter output for cleaned fluid, the bypass valve is located in the region of the cover part and is in a fluid connection to the fluid guide at the filter input. Compared to the conventional positional arrangement provided for bypass valves, the bypass valve is thus offset away from the filter sump towards the head side, i.e., into the immediate region of the filter input, so that at high dynamic pressures the pressure decrease takes place directly at the filter input. In this way, operating reliability, especially during cold starting phases, is increased.

Preferably, the filter housing has a bottom-side tank connection for the discharge of excess reflux amounts to the tank, the back pressure valve in the bottom region of the filter housing adjacent to the tank connection for blocking or clearing a fluid connection being located between the filter output and tank connection.

Exemplary embodiments in which the replenishing valve is located underneath the back pressure valve, nearer the tank connection, in the bottom region of the filter housing, are especially suitable for tank installation of the device since separate feed lines to the replenishing valve are not necessary.

The device can be advantageously designed such that the filter medium of the filter element, through which flow can take place from outside to inside during filtration, surrounds a coaxial, fluid-permeable support pipe, within and at a distance from the latter there being a concentric interior pipe, and the cleaned fluid which is located on its exterior on the end of the interior pipe being fluid-connected to the units located in the bottom region of the filter housing in the form of the back pressure valve and of the replenishing valve. In this way, within the filter element a pipe-in-pipe system is formed in which the interior pipe, whose exterior borders the clean side during filtration, with its pipe exterior forms the fluid connection to the bottom-side valve units. This pipe-in-pipe construction leads to an especially compact, slender body of the device with high inherent stability even when potential pressure fluctuations occur during operation.

In these exemplary embodiments, preferably, the bottom region of the filter housing can have a pipe body which continues the interior pipe of the inserted filter element and on which the valve bodies of the back pressure valve and replenishing valve are guided for opening and closing movements which are opposite one another. These valve units thus form a direct coaxial extension on the bottom of the filter element.

In especially advantageous exemplary embodiments, the bypass valve is integrated into the head-side end cap of the filter element, in the cap at least one bypass channel being formed which with the filter element inserted connects the filter input of the cover part of the filter housing to the input side of the bypass valve.

Preferably, the bypass valve is a spring-loaded spool valve whose spool is guided in a hollow-cylindrical valve housing which is concentric to the longitudinal axis and during opening, which is dictated by the dynamic pressure, forms the fluid connection between the bypass channel and interior of the valve housing.

An especially compact construction is produced when the interior pipe of the filter element is a bypass pipe which on the inside forms at least part of the fluid connection between the interior of the valve housing of the bypass valve and the tank connection located in the bottom region. In this respect, the valve housing of the bypass valve can form a direct fluid connection to the facing end of the interior pipe so that with the bypass valve opened the pressure decrease out of the valve housing takes place directly through the interior pipe which is used as the bypass pipe to the tank connection.

The invention offers an especially advantageous option for changing the hydraulic circuit as desired. While, when using the interior pipe as the open bypass pipe, when the bypass valve is triggered, the pressure drop takes place directly to the tank by way of the interior pipe, the circuit can also be made such that the fluid, which is flowing away when the bypass valve opens, does not travel to the tank, but rather out of the valve housing directly to the clean side of the filter element, i.e., to the filter output of the device. In this case, the interior pipe of the filter element is closed, and the valve housing has an outflow region which, with the bypass valve open, forms the fluid connection from the interior of the valve housing to the filter output in the cover part.

In this connection, the outflow region of the bypass valve can be formed by openings in the valve housing cover, which, as a head-side, round plug, forms the support of the closing spring of the bypass valve. For the fluid, which is flowing off by way of the openings in the valve housing cover, the flow conditions are especially favorable when the openings in the valve housing cover are made in an arrangement which is distributed in a star shape and with a trapezoidal opening surface.

In particular, in cases where the interior pipe is closed and the fluid is flowing directly to the filter output when the bypass valve has been triggered, a protective bypass screen is preferably integrated into the pertinent fluid guide in the cover part, so that the fluid which is traveling to the clean side is free of at least coarser dirt.

In order to prevent the danger of dirt being able to travel by way of replenished fluid to the clean side and thus to the connection of the feed pump of the downstream hydrostatic circuit when the replenishing valve is opened, there is preferably a replenishment screen arrangement which is inserted into the fluid path between the replenishment openings of the replenishing valve and the tank connection.

The subject matter of the invention is also a filter element for a filter device according to one of claims 1 to 19, the filter element having the features specified in claim 20.

The invention is detailed below using the exemplary embodiments shown in the drawings.

FIGS. 1 to 3 show symbol representations of the circuit of the components of a first embodiment and a second embodiment and a third embodiment of the filter device according to the invention, respectively;

FIG. 4 shows a detached longitudinal section of only the upper, cover-side partial section of the filter device in an embodiment which corresponds to the circuit of FIG. 1, but with a protective bypass screen that is additionally provided by way of comparison;

FIG. 5 shows a longitudinal section which shows only the bottom-side, lower partial section of the embodiment of the device shown in FIG. 4;

FIG. 6 shows a representation similar to FIG. 4, the head-side partial section, however, being shown turned by 90 degrees compared to FIG. 4;

FIG. 7 shows a longitudinal section of one embodiment of the filter device drawn on a smaller scale compared to FIGS. 4 to 6 in a circuit of the embodiment which corresponds to FIG. 3;

FIG. 8 shows a longitudinal section of only the filter element of one exemplary embodiment of the filter device according to the invention in an embodiment which corresponds to the circuit from FIG. 1, and

FIG. 9 shows a perspective oblique view of the valve housing cover of the bypass valve of the exemplary embodiment from FIG. 7.

In the circuit examples shown in FIGS. 1 to 3, a connection to which a fluid reflux amount is supplied from working hydraulics, which are not shown, is designated as A. By way of a connection designated as B, the feed pump of a compensator which is not shown, for example a hydrostatic traveling mechanism (not shown), is supplied with the amount of fluid required as the fill amount. This amount of fluid is removed on the clean side 1 of a filter element 3, i.e., from the reflux flow which has been filtered in full flow and which exceeds the filling flow that is required by the feed pump of the downstream compensator. The clean side 1 of the filter element 3 is connected by way of a back pressure valve V₁ to the tank connection T. The back pressure valve V₁ which can be opened by pressure actuation is set to an opening pressure which ensures that on the clean side 1 and thus on the connection B a pressure level is maintained at which the feed pump of the downstream compensator can remove the required amount by way of the connection B. On a standard basis, the back pressure valve V₁ is set to an opening pressure of 0.5 bar.

Downstream of the back pressure valve V₁, a replenishing valve V₃ which can be opened likewise by pressure actuation is connected and is set to a low opening pressure of roughly 0.05 bar and opens when the pressure of the reflux amount has dropped on the clean side 1 and therefore for operation of the suction pump which is connected downstream of the connection B fluid needs to be replenished via the replenishing valve V₃ from the tank as an emergency function. When the dynamic pressure prevailing on the filter element 3 exceeds a threshold value, which is recognized, for example, by a fouling indicator VA which is connected to the dirty side at the connection A, a bypass valve V₂, which can be actuated by pressure, opens for a pressure reduction from connection A, and for the circuit from FIG. 1, towards the tank. Conventionally, a dynamic pressure of roughly 2 bar prevailing on the filter element 3 is the opening pressure for the bypass valve V₂. In FIG. 1, in which the back pressure valve V₁ is set to an opening pressure of 0.5 bar, the bypass valve V₂ would accordingly be set to an opening pressure of 2.5 bar.

The versions of FIGS. 2 and 3 differ from FIG. 1 in that the pressure drop from connection A does not take place by way of the bypass valve V₂ towards the tank, but by way of the clean side 1 of the filter element 3 and by way of the back pressure valve V₁ to the tank connection T, whereby the bypass valve V₂ can be set to an opening pressure of 2.0 bar on a standard basis.

The circuit version shown in FIG. 3 corresponds to that from FIG. 2, aside from the fact that a protective bypass screen 5—also in the from of a filter element—is located in the flow path of the fluid which is flowing through the bypass valve V₂ so that the connection B is protected from fouling even when the bypass valve has been opened. As has been shown, the circuit version of FIG. 2 in which the filter element 3 can be directly bypassed by the opened bypass valve V₂, without the fluid flowing away via the bypass valve having to flow through a protective screen or protective filter, is advantageous in those cases in which the fluid is an oil of high viscosity, as is the case, for example, during cold starting phases: As is detailed below, the invention makes it easy to switch the circuit between the operating modes shown in FIG. 1 or those in FIGS. 2 and 3.

FIGS. 4 and 6 each show the head-side end region of a filter housing 7 of the device in an embodiment in which a protective bypass screen 5 or a bypass filter element is present. In these figures the head-side cover part of the filter housing 7 is designated as 9 and the upper end termination which is screwed to the cover part 9 is designated as 11. After the end termination 11 is unscrewed, the filter element 3 of a largely circular cylindrical shape can be placed in the hollow cylinder-like main body 15 which in its bottom region 17, see FIG. 5, forms an element receiver 19 in which a ring body 21 of the filter element 3 can be held, forming a seal. The ring body 21 forms an extension of the bottom-side end cap 23 of the filter element 13, which extension is coaxial to the longitudinal axis 25 of the filter element 13, the end cap 23 forming an enclosure for the lower end of the filter medium 27 of the filter element 3. The ring body 21 surrounds the opening region 29 of the end cap 23. This region 29 is fluid-connected to the inner filter cavity 31 of the filter element 3, which cavity forms the clean side during filtration.

FIG. 4 shows the upper region of the device in a position in which the filter output 33 that corresponds to the connection B in FIGS. 1 to 3 is visible. Conversely, FIG. 6 shows this section of the device in the rotary position in which the filter input 35 can be seen. As can likewise be taken from the latter figures, with the filter element 3 inserted, the filter input 35 is fluid-connected by way of fluid guides 51 to the exterior 37 of the filter medium 27; the exterior forms the dirty side during filtration, and through it medium flow takes place during filtration from the exterior to the inner filter cavity 31, which forms the clean side. The upper, head-side end cap 39 of the filter element 3 forms not only the enclosure for the upper end of the filter medium 27, but a hollow cylinder-shaped valve housing 41 for a bypass valve and a support for an interior pipe 43 which is concentric to the longitudinal axis 25 and which runs, leaving open the filter cavity 31 which forms the clean side, at a distance from the support pipe 45 on whose exterior the filter medium 27 rests. The filter cavity 31 which forms the clean side is connected via passages in the end cap 39, of which FIG. 4 shows one which is designated as 47, to a fluid guide 49 in the cover part 9 which leads to the filter output 33, i.e., to the connection B. The exterior 37 of the filter medium 27 which forms the dirty side is in turn connected in the cover part 9 to the fluid guide 51 which is connected in the cover part 9 to the filter input 35, i.e., the connection A. As is apparent from FIG. 6, bypass channels 53 extend from the fluid guide 51 to the interior of the valve housing 41. In the valve housing 41, the valve spool of the bypass valve V₂, which is made as a spool valve is movably guided. The valve housing 41 forms a hollow cylinder which is concentric to the longitudinal axis 25 and on whose inside wall the valve spool 55 is guided that has an end-side closing edge 57 which, when the valve spool 55 has been pushed into the open position, clears the fluid path from the bypass channels 53 into the interior of the valve housing 41 and thus into the interior pipe 43. In the exemplary embodiments in which, as shown in FIGS. 4 to 6, the interior pipe 43 is open, i.e., is passable, when the bypass valve V₂ has been opened, the pressure can drop by the fluid flowing away through the interior pipe 43 to the tank connection T. The valve spool 55 is pretensioned into the closed position by means of a compression spring 59 which is clamped between the valve spool 55 and a cover 61 which forms the end-side termination of the valve housing 41. In the exemplary embodiments with the through interior pipe 43 (FIGS. 4 to 6 and 8) the valve housing cover 61 is a round plug in the form of a closed cap.

As already mentioned, the circuitry of the device can be easily changed such that the fluid which is flowing away via the bypass valve V₂ does not travel directly to the tank, as is the case in the circuit of FIG. 1, but that according to the circuits from FIGS. 2 and 3 with the bypass valve V₂ opened, the fluid which is flowing away travels to the clean side 1 of the filter element 3 and can travel from there via the back pressure valve V₁ to the tank connection T. In order to execute the circuit in this way, i.e., to shift the device into the state shown in FIG. 7, only two measures are necessary, specifically the closure of the interior pipe 43, for example, by means of the crosspiece designated as 63 in FIG. 7. Second, instead of the housing cover 61 in the form of a closed cap, a housing cover 65 which is open on the top is used, as is shown separately in FIG. 9. As is clearly to be seen in FIG. 9, the housing cover has outflow openings 67 of a trapezoidal opening surface, which openings are arranged in a star shape, and via which fluid can flow out of the valve housing 41, without stronger flow resistance having to be overcome, to the fluid guide 49 and thus to the filter output 33 when the valve spool 55 against the force of the spring 59 executes an opening motion in which the closing edge 57 forms an opening gap so that fluid flows into the valve housing 41 out of the bypass channels 53.

For viscous fluids, for example oil with high viscosity which prevails during cold starting phases, the direct flow connection between the filter input 35 and filter output 33 that is formed in this way with the bypass valve V₂ opened is advantageous, especially when the protective bypass screen 5 or filter is not connected upstream of the bypass channels 53. On the other hand, using a protective bypass screen or filter avoids the danger that with the bypass valve V₂ opened dirt can travel to the filter output 33. In the exemplary embodiments shown in FIGS. 4 to 7, a protective bypass screen 5 each is arranged within a bell-shaped intermediate body 69 such that it is located in the fluid path between the fluid guides 51 and the bypass channels 53.

The bell-shaped intermediate body 69 within the cover part 9 separates the fluid guides 49 and 51 from one another and at the same time forms the seal of the upper end cap 39 of the filter element 3.

FIGS. 5 and 7 show the lower bottom region 17 which is connected to the element receiver 19; its details are shown most clearly in FIG. 5. As illustrated, the interior pipe 43 of the filter element 3 is extended down towards the tank connection T. The filter cavity 31 of the filter element 3 which forms the clean side is connected to a pipe body 73 by way of the opening regions 29 in the end cap 23 of the filter element. To form a spring housing, the pipe body is surrounded by a hollow cylindrical spring housing 75 which is concentric to the longitudinal axis. In this spring housing there are a closing spring 77 for the back pressure valve V₁ and a spring 79 for the replenishing valve V₃, the two compression springs surrounding the pipe body 73. The back pressure valve V₁ has an axially movable valve body 81 which is guided on the exterior of the pipe body 73 and with a hollow cylindrical extension 83 on the inside of the spring housing 75. The latter has a cup bottom 85 through which the pipe body 73 extends, and several replenishment openings 87. This cup bottom 85 forms the valve seat for the valve body 86 of the replenishing valve V₃, which body is made as a ring plate.

The valve body 81 of the back pressure valve V₁ interacts with the ring body 21 on the end cap 23 of the inserted filter element 3 as a valve seat, against which the valve body 81 is pressed by the closing spring 77. When the valve body 81 is raised against the force of the closing spring 77, fluid flows out of the interior 31, i.e., the clean side of the filter element 3, via the open region 29 of the end cap 23 along the exterior of the spring housing 75 directly to the tank connection T. When no filter element 3 has been inserted into the device, the valve body 81 with a radially outlying valve disk edge 89 forms the seal of the device relative to the tank connection side by the valve disk edge 89 sealing against the element receiver 19 of the main housing part 15.

The interior of the spring housing 75 is connected by fluid to the filter interior 31, i.e., to the clean side, by way of the fluid passages 91, which are made in the valve body 81 and by way of the opening regions 29 of the end cap 23. Towards this clean side, when the valve body 86 which is made as a ring plate is raised against the force of the closing spring 79 away from the replenishment openings 87, fluid can be replenished from the side of the tank connection T in order to travel by way of the fluid passages 91 of the valve body 81 to the cavity 31 and thus to the clean side and to the connection B.

As can likewise be taken from FIG. 5, the underside of the body 85 of the spring housing 75 is connected to a screen housing 93 whose interior 95 borders the replenishment openings 87. Between the interior 95 and its exterior, i.e., the tank connection T, there is a replenishment screen 97 or replenishment filter so that in the replenishment process direct unfiltered replenishment of fluid from the tank connection T does not take place.

As can be taken from FIGS. 5 and 7, the bottom region 17 of the main housing body 15 is connected to an extension pipe 99 which can be made as a submersible pipe of the desired length, for example in tank installation, depending on installation conditions.

FIG. 8 shows a filter element 3 separately; it has a continuously open interior pipe 43 and accordingly a valve housing cover 61 in the form of a closed cap. As is apparent, the upper end cap 39 forms a pipe socket 98 which projects appropriately into the end of the interior pipe 43 and whose opening edge 100 interacts with the closing edge 57 of the valve spool 55. When the closing edge 57 is raised off the edge 100, the fluid path is thus cleared from the bypass channels 53 into the interior of the valve housing 41 and into the interior of the interior pipe 43 which now acts as a bypass pipe towards the tank side.

With the filter device according to the invention, a novel pipe-in-pipe system is formed in which the bypass pipe is centrally guided through the element support pipe and the position of the bypass valve changes from the “filter sump” upward. By closing the bypass pipe and another bypass closing cover, the switching logic of the filter device can be easily changed, i.e., the bypass goes directly to the intake side. This is possible among other things by using the novel, internally hollow bypass valve in a spool construction. Furthermore, with the filter device according to the invention it is ensured that without the filter element inserted there is no buildup of feed pressure; this constitutes an indication of a missing filter element. Due to the special trapezoidal shape of the cross channels, the novel bypass cap in a so-called cross flow construction prevents the cross section of the filtered oil from being constricted so that energy losses are avoided in filter operation. 

1. A filter device, particularly a reflux vacuum filter, with at least one filter housing (7) in which at least one filter element (3) which defines a longitudinal axis (25) can be accommodated, and with at least two valve units, especially in the form of a bypass valve (V2) and a back pressure valve (V₁), characterized in that the indicated valve units are arranged concentrically to the longitudinal axis (25) of the respective filter element (3) along this longitudinal axis (25).
 2. The filter device according to claim 1, characterized in that there is a third valve unit in the form of a replenishing valve (V₃) in an arrangement concentric to the longitudinal axis (25) of the filter element (3).
 3. The filter device according to claim 1, characterized in that the filter housing (7) has a head-side cover part (9) with fluid guides (49, 51) which border the upper end region of the inserted filter element (3) as well as at least one filter input (35) for reflux fluid, and at least one filter output (33) for cleaned fluid, and that the bypass valve (V₂) in the region of the cover part (9) and in a fluid connection to the fluid guide (51) is located at the filter input (35).
 4. The filter device according to claim 3, characterized in that the filter housing (7) has a bottom-side tank connection (T) for the discharge of excess reflux amounts to the tank and that the back pressure valve (V₁) in the bottom region (17) of the filter housing (7) adjacent to the tank connection (T) for blocking or clearing a fluid connection is located between the filter output (33) and tank connection (T).
 5. The filter device according to claim 4, characterized in that the replenishing valve (V₃) is located underneath the back pressure valve (V₁), nearer the tank connection (T), in the bottom region (17) of the filter housing (7).
 6. The filter device according to claim 1, characterized in that the filter medium (27) of the filter element (3), through which medium the flow can take place from outside to inside during filtration, surrounds a coaxial, fluid-permeable support pipe (45), that within and at a distance from the latter there is a concentric interior pipe (43) and that the cleaned fluid which is located on its exterior is fluid-connected on the end of the interior pipe (43) to the valve units located in the bottom region (17) of the filter housing (7) in the form of the back pressure valve (V₁) and of the replenishing valve (V₃).
 7. The filter device according to claim 6, characterized in that the bottom region (17) of the filter housing (7) has a pipe body (73) which continues the interior pipe (43) of the inserted filter element (3) and on which the valve bodies (81 and 86) of the back pressure valve (V₁) and replenishing valve (V₃) are movably guided for opening and closing movements which are opposite one another.
 8. The filter device according to claim 7, characterized in that closing springs (77, 79) of the two indicated valves surround the pipe body (73).
 9. The filter device according to claim 8, characterized in that the valve body (81) of the back pressure valve (V₁) has a hollow cylindrical extension (83) which extends along the exterior of the closing springs (77, 79) and which is guided outside on the inside of a spring housing (75) which in the form of a cup with a cylindrical wall concentrically surrounds the pipe body (73) and whose bottom (85) is penetrated by the pipe body (73) whose end forms the tank connection (T).
 10. The filter device according to claim 9, characterized in that the bottom (85) of the spring housing (75) forms the valve seat for a ring plate (86) which forms the valve body of the replenishing valve (V₃) and by which the replenishment openings (87) in the bottom (85) of the spring housing (75) can be blocked or cleared.
 11. The filter device according to claim 10, characterized in that the valve body (81) of the back pressure valve (V₁) has fluid passages (91) which connect the interior of the cup of the spring housing (75) to the clean side which is located on the exterior of the pipe body (73) and of the interior pipe (43) of the inserted filter element (3).
 12. The filter device according to claim 3, characterized in that the bypass valve (V₂) is integrated into the head-side end cap (39) of the filter element (3), in which at least one bypass channel (53) is formed which with the filter element (3) inserted connects the filter input (35) of the cover part (9) of the filter housing (7) to the input side of the bypass valve (V₂).
 13. The filter device according to claim 12, characterized in that the bypass valve is a spring-loaded spool valve whose spool (55) is guided in a hollow-cylindrical valve housing (41) which is concentric to the longitudinal axis (25) and during opening which is dictated by the dynamic pressure forms the fluid connection between the bypass channel (53) and the interior of the valve housing (41).
 14. The filter device according to claim 13, characterized in that the interior pipe (43) of the filter element (3) is a bypass pipe which on the inside forms at least part of the fluid connection between the interior of the valve housing (41) of the bypass valve (V₂) and the tank connection (T) which is located in the bottom region (17).
 15. The filter device according to claim 14, characterized in that the interior pipe (43) of the filter element (3) is closed, and that the valve housing (41) has an outflow region (65, 67) which with the bypass valve (V₂) opened forms the fluid connection from the interior of the valve housing (41) to the filter output (33) in the cover part (9).
 16. The filter device according to claim 15, characterized in that the outflow region is formed by openings (67) in the valve housing cover (65) which as a head-side, round plug forms the support of the closing spring (59) of the bypass valve (V₂).
 17. The filter device according to claim 16, characterized in that the openings (67) in the valve housing cover (65) are made in an arrangement which is distributed in a star shape and with a trapezoidal opening surface.
 18. The filter device according to claim 12, characterized in that a protective bypass screen (5) or bypass filter which is located in the respective bypass channel (53) is integrated into the pertinent fluid guide (51) of the cover part (9).
 19. The filter device according to claim 9, characterized in that a carrier (93) which forms an enclosure on the bottom (85) of the cup of the spring housing (75) and an extension of the pipe body (73) is designed for a replenishment screen arrangement (97) or replenishment filter which is inserted into the fluid path between the replenishment openings (87) of the replenishing valve (V₃) and the tank connection (T).
 20. A filter element for a filter device according to claim 1, with a filter medium (27) which surrounds a fluid-permeable support pipe (45) which defines a longitudinal axis (25), with one bottom-side cap and one head-side end cap (23 and 39) each of which forms one end enclosure of the filter medium (27), with an interior pipe (43) which is arranged within and at a distance from the support pipe (45) concentrically to the longitudinal axis (25), and whose bottom-side end extends through an open region (29) of the bottom side end cap (23), and with a bypass valve (V₂) which is integrated into the head-side end cap (39) in the form of a spool valve with a spring-loaded valve spool (55) which is guided in a valve housing (41) which is concentric to the longitudinal axis (25). 